Automotive air conditioning systems typically consist of a compressor to increase the pressure of refrigerant, a condenser or heat exchanger to transfer thermal energy from the high pressure refrigerant to the surrounding environment, an expansion device to throttle the high pressure refrigerant at constant enthalpy to a lower temperature, and an evaporator to transfer thermal energy from the conditioned space to the refrigerant. Associated interconnecting lines, tubing, and hoses contain and convey refrigerant between the components of the system. In most modern automotive air conditioning systems, the compressor is engine mounted so that the engine power train can conveniently drive the compressor via belts, gears, etc., while the heat exchanger components are body mounted in close proximity to the working air-side fluid. For example, the condenser is mounted in front of the vehicle, ahead of the radiator so that a sufficient quantity of cooler air is directed over its heat transfer surfaces for adequate performance during most operating conditions. Another example is the evaporator which is mounted inside of a plastic case or module near the passenger compartment so that air handling and ducting of fresh, conditioned air is facilitated easily. As a result of these packaging constraints, it is often necessary to locate the threaded connectors, which are on the ends of the lines, tubing and hoses, in areas that are not easily accessible to the assembly operator. One method of reducing the amount of accessible area needed to assemble these connections is the use of a block fitting which uses a single bolt to draw two halves of the connection together. In this manner, only clearance for a socket and wrench extension is needed.
The conventional O-ring style block is currently used on an evaporator. An aluminum inlet pipe and an aluminum outlet pipe are welded to the evaporator core on one end and are welded or brazed to the back side of an evaporator block fitting. An inlet port and outlet port are internally machined into the front surfaces of the evaporator block fitting in such manner that a nearly vertical O-ring sealing surface is formed inside the outlet port and the inlet port. On the opposing side of the connection, a plate-like customer block receives the formed aluminum end of the suction hose and the liquid line. The liquid line fits into a slot in the customer block. The purpose of the slot is to eliminate the need to precision machine the center-to-center distance dimensioned between the suction hose and the liquid line end in the customer block. In assembling the block, two toroidally-shaped elastomeric O-rings are slidably installed onto the formed male ends of the aluminum pipes. The connection halves are then brought together to engage the male pipe ends into the machined bores in the evaporator block. An externally threaded hexagon head fastener is then inserted through a centrally located hole in the customer block to engage an internally threaded hole in the evaporator block.
Problems are associated with the use of the conventional O-ring style block fitting.
First, the O-rings are not observable by the assembler as the halves of the joint are brought together. Consequently if an O-ring is misaligned so as to be pinched or forced out of the female sealing cavity, the problem may go unnoticed until a refrigerant leak occurs during operation of the air conditioning system.
Secondly, the lines connecting the customer block to the compressor and to the condenser are often not sufficiently flexible to permit an easily controlled insertion into the female seating cavities. Consequently, angularity may be introduced between the longitudinal axes of the ports in the evaporator block and the longitudinal axes of the ports in the customer block. Such angularity often causes uneven elastomeric compression on conventional O-ring type block fitting joints during insertion, resulting in cut, pinched, or otherwise damaged O-rings.
Thirdly, the male end forms, or terminations, used with conventional O-ring style line connections are typically formed via an upsetting process onto the ends of aluminum or steel tubes. These formed ends typically have characteristic microscopic disparities, or "tooling marks," that run perpendicular to the direction of the seal itself as a consequence of the forming operation. These microscopic disparities subtract from the contact area between the mating sealing surfaces and the seal itself, resulting in greater long-term refrigerant leakage than would be possible with a design having concentrically parallel, or circumferential "tooling marks".
A sealing washer compressor connection has been used, but is not directly applicable to the evaporator without significant changes. In the sealing washer compressor connection, the cast housing of the compressor has a nearly figure-8 shaped portion or boss for the female sealing cavities of the suction port and the discharge port of the compressor. The other half of the connection consists of a compressor block that has machined onto the front face two raised, stepped surfaces on the suction and discharge sides respectively, the outboard plane of which serves as the sealing surfaces. The back side of the compressor block has two counter bores or sockets machined into it for reception and welding of the suction pipe and the discharge pipe thereto. Two sealing washers are slidably installed onto the machined male diameters on the front side of the compressor block until they bottom out or touch the plane of the raised faces on the compressor block. The sealing washers each consist of a metallic retainer, punched, coined and optionally splined that has bonded to the inner periphery an elastomeric material that is compatible with the refrigerant system and the fluids contained therein. An externally threaded hexagon head attachment bolt is then inserted through a hole in the compressor block to engage an internally threaded hole in the compressor to firmly hold the two halves of the connection together when tightened. This type of connection is not directly applicable to evaporator or condenser connections because the liquid line and suction lines typically are routed in a circuitous manner in different paths that require separate connections at the evaporator or condenser. Furthermore, the precision design of port-to-port dimensions in a one-piece compressor block connection may be too costly for use in multi-port sealing washer block connections.